…I speak, of course, of the legs of a triathlon. There are three: swim, bike run. Let’s break it down, shall we?

Swim
Legend goes that triathlon organizers built triathlon to be in the order it is now because the swim is the area that’s the most dangerous. You don’t want tired, zoned-out people flailing around in deep water. It’s bad juju, and bad liability, to boot. So they put the swim first, which means you get on your bike cold and wet. Well, that can’t be helped, and you dry off pretty fast, anyway.
The swim leg is most difficult for many people. Many triathlon organizers, if they make use of cut-offs (times requiring you to be done with specific legs, or the race itself, at a given time) give you the most time to do the swim, proportionately. For instance, I’ll probably finish the swim time in about an hour and a half, if I’m lucky and do everything right. The pros will finish in under an hour. But the swim cutoff time is still a whopping 2 hours and 20 minutes.(This is what a swim start looks like. Messy, splashy, and fun. Also, confusing.)

Some things to learn
There’s actually not too much to say about the swim; really, it’s just something you have to get through.
More and more sprint race directors have cut the swim to 400 meters, or about a quarter of a mile, a distance that even only a fairly decent swimmer can get through in 10 minutes. I know people who have done that distance entirely on their backs, or using the breast stroke. Heck, I know folks who have done 800 meters in a sprint race on their backs. The point is, learn to do the crawl. It’s much more efficient, and you’ll be able to see.
Another skill you’ll need to learn is sighting. It’s the art of looking up every once in awhile to see where you’re going. In a pool, you’ve got the lap lines and the pool wall to guide you. In a murky lake, no such luck. You only need to sight every six or so strokes, but make sure you learn to do it. Getting lost in the swim portion of a triathlon is fodder for a lot of bad jokes at your expense.
Learn, as well, to breathe bilaterally. The theory is that it will help to keep you going in a straight line if you’re not just breathing to one side all the time, but I’ve found that it also keeps my neck muscles loose in a long swim. At the very least, it’s something else to focus on, which helps me to get through the time better.

Some things to expect
When you do get to your first triathlon, be sure to spend some time in the water before the race starts. A lot of people freeze up when they get into the open water. I’m not saying that this is going to happen to *you*, but you might as well prevent it if you can.
Then there’s the actual start of the race.
It feels like this:Clif Bar on YouTube
No, I’m not kidding. Just be ready for it. There’s a lot of people, all vying for their spot to swim in, and you need to expect that you might be kicked.
You might experience some vertigo coming out of the water. This is normal. Once you get out of the water, start unzipping your wetsuit and struggling out of it. I’ve seen racers apply Body Glide to their lower arms and legs, both under the wetsuit and on the outer of the wetsuit itself, so it’ll slide against itself better and be easier to remove. Do practice taking your wetsuit off a couple of times, at least, in a hurry. You don’t want to be struggling in the transition area and losing valuable time. Don’t forget to pull off your goggles and swim cap.